Circular ring-shaped member for plasma process and plasma processing apparatus

ABSTRACT

A plasma processing apparatus includes a processing chamber the inside of which is maintained in a vacuum; a mounting table configured to mount a target substrate and serve as a lower electrode in the processing chamber; a circular ring-shaped member provided at the mounting table so as to surround a peripheral portion of the target substrate; an upper electrode arranged to face the lower electrode thereabove; and a power feed unit for supplying a high frequency power to the mounting table. The apparatus performs a plasma process on the target substrate by plasma generated in the processing chamber. The circular ring-shaped member includes at least one ring-shaped groove configured to adjust an electric field distribution to a desired distribution in a plasma generation space, and the groove is formed in a surface of the circular ring-shaped member and the surface is on an opposite side to the plasma generation space.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2009-128355 filed on May 27, 2009, and U.S. Provisional Application Ser.No. 61/228,636 filed on Jul. 27, 2009, the entire disclosures of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a circular ring-shaped member for aplasma process configured to surround a peripheral portion of a targetsubstrate on which a plasma process is performed in a plasma processingchamber, and a plasma processing apparatus including the same.

BACKGROUND OF THE INVENTION

In a manufacturing process of a semiconductor device or a FPD (FlatPanel Display), there has been widely used a plasma processing apparatusfor etching, deposition, oxidation, sputtering, or the like. As one ofthe plasma processing apparatuses, there has been known a plasma etchingapparatus in which an upper electrode and a lower electrode are arrangedparallel to each other within a processing vessel or reaction chamber, atarget substrate (semiconductor wafer, glass substrate or the like) ismounted on the lower electrode, and a high frequency voltage for plasmageneration is applied to either or both of the upper electrode and thelower electrode via a matching unit in most cases.

Generally, a plurality of gas discharge holes is provided in the upperelectrode and an etching gas excited into plasma is discharged to theentire substrate through the gas discharge holes so as to etch theentire surface of the target substrate at the same time.

Typically, in a parallel plate type plasma etching apparatus, an upperelectrode and a lower electrode are arranged parallel to each other, anda high frequency voltage for generating plasma is applied to the upperelectrode or the lower electrode via a matching unit. Electronsaccelerated by a high frequency electric field between both theelectrodes, secondary electrons emitted from the electrodes, or heatedelectrons collide with molecules of a processing gas and are ionized, sothat the processing gas is excited into plasma. By radicals or ions inthe plasma, a required microprocessing such as an etching process isperformed on a surface of a substrate.

As semiconductor integrated circuits are miniaturized, high densityplasma under a low pressure is required in a plasma process. Forexample, in a capacitively coupled plasma processing apparatus, a plasmaprocess of a higher efficiency, a higher density, and a lower bias poweris required. Further, as semiconductor chips become large-sized andtarget substrates have large diameters, plasma of a larger diameter isrequired, and, thus, chambers (processing vessels) also become scaledup.

However, in the large-diameter plasma processing apparatus along withthe large-diameter target substrate, an intensity of an electric fieldat a central portion of an electrode (upper electrode or lowerelectrode) tends to be higher than that of an electric field at an edgeportion thereof. As a result, there is a problem in that a density ofthe generated plasma at the central portion of the electrode isdifferent from a plasma density at the edge portion thereof. Therefore,a resistivity of the plasma becomes low at a portion in which plasmadensity is high, and a current is also concentrated on a correspondingportion of a facing electrode. Accordingly, there is a problem in that anon-uniformity of the plasma density becomes serious.

Furthermore, as the chamber becomes scaled up along with thelarge-diameter target substrate, there is a problem in that a plasmadensity at a central portion of the target substrate is different from aplasma density at a peripheral portion thereof in an actual etchingprocess due to a flow of a processing gas caused by a temperaturedistribution.

The non-uniformity of the plasma density causes a difference in anetching rate of the target substrate, and particularly, it causes adeterioration of a device yield obtained from the peripheral portion ofthe target substrate.

In this regard, various researches for a configuration of an electrodehave been conducted until now. For example, in order to solve theabove-described problem, there has been known a technique of providing ahigh resistance member at a central portion of a main surface of a highfrequency electrode (see Patent Document 1). According to thistechnique, the high resistance member is provided at the central portionof the main surface (plasma contact surface) of the electrode connectedwith a high frequency power supply, so that an intensity of an electricfield at the central portion of the main surface of the electrode isrelatively lowered as compared to an intensity of an electric field atan outer peripheral portion thereof. Therefore, non-uniformity of anelectric field distribution can be corrected.

Further, in a plasma processing apparatus disclosed in Patent Document2, a dielectric member is embedded in a main surface of an electrodefacing a processing space such that impedance against a high frequencypower supplied from the main surface of the electrode to the processingspace is relatively high at an central portion of the electrode andrelatively low at an edge portion of the electrode. With thisconfiguration, uniformity of an electric field distribution can beimproved.

Meanwhile, in order to improve uniformity of a plasma densitydistribution at the edge portion of a target substrate, the plasmaprocessing apparatus includes a circular ring-shaped member such as afocus ring, provided so as to surround an outer periphery of a wafermounted on a mounting table within the processing chamber. By way ofexample, the focus ring may have a double-circle structure including aring-shaped inner focus ring positioned on inner side and a ring-shapedouter focus ring positioned so as to surround an outer periphery of theinner focus ring. Generally, the inner focus ring may be made of aconductive material such as silicon and the outer focus ring may be madeof an insulating material such as quartz.

The inner focus ring has a function to concentrate plasma on the wafer,and the outer focus ring serves as an insulator confining the plasma onthe wafer.

During a plasma process, a temperature of the outer focus ring increasesdue to heat transferred from the plasma. If the temperature is notstable, a radical density in the vicinity of the outer focus ringbecomes non-uniform and a plasma density at an outer peripheral portionof the wafer becomes non-uniform as well. As a result, an effect of theplasma process at the central portion of the wafer is different fromthat at the outer peripheral portion thereof, and, thus, it becomesdifficult to perform the plasma process on the wafer uniformly.

Therefore, in Patent Document 3, a ring-shaped groove is formed in anouter focus ring so as to reduce a heat capacity of the outer focusring, so that a temperature of the outer focus ring is rapidly increasedand is easily maintained high by heat transferred from plasma. With thisconfiguration, uniformity of the plasma density at a peripheral portionof the wafer can be achieved and deposits on the focus ring can beremoved at the earliest stage of a production lot.

Patent Document 1: Japanese Laid-open Publication No. 2000-323456

-   Patent Document 2: Japanese Laid-open Publication No. 2004-363552-   Patent Document 3: Japanese Laid-open Publication No. 2007-67353

However, in a high frequency discharge type plasma processing apparatusas disclosed in Patent Documents 1 and 2, since a high resistance memberis provided at a central portion of a main surface of a high frequencyelectrode, there is a problem in that a large quantity of a highfrequency power is consumed (energy loss) due to Joule's heat.

In accordance with a technique in which a dielectric member is embeddedin the main surface of an electrode as disclosed in Patent Documents 1and 2, a characteristic of an impedance distribution on the main surfaceof the electrode is determined by a material and a shape profile of thedielectric member. Therefore, there is a problem in that such atechnique can not respond flexibly to various kinds of processes orvariation of process conditions.

Further, in Patent Document 3, a groove is formed in an outer focus ringso as to reduce a heat capacity. Accordingly, uniformity of a plasmadensity distribution at a peripheral portion of a wafer can be obtaineddue to increase and stabilization of a temperature in a short time.

However, in order to obtain the uniformity of the plasma densitydistribution at the peripheral portion of the wafer, not only thetemperature needs to be stabilized but a distribution or an intensity ofan electric field at the peripheral portion of the wafer also need to beadjusted to a desired level.

In Patent Document 3, by providing the groove in the outer focus ring soas to reduce the heat capacity, stability of the temperature can beobtained. However, the uniformity of the plasma density distributioncaused by the stability of the temperature is obtained only while thetemperature is stabilized, which does not mean that the distribution orintensity of the electric field is adjusted to a desired level.Therefore, in Patent Document 3, a problem of adjusting the electricfield distribution to a desired level can not be solved.

Furthermore, in Patent Document 3, the groove is formed in the outerfocus ring so as to reduce the heat capacity, so that uniformity of theplasma density distribution can be obtained. However, in order to securean etching rate or a deposition rate of a desired level at the endportion of the wafer, an electric field distribution on a top surface inthe vicinity of the end portion of the wafer needs to be adjusted to adesired level, which has not been solved in Patent Document 3.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, the present disclosure provides a circularring-shaped member for a plasma process capable of improving uniformityand production yield in the plasma process by adjusting an electricfield distribution at a peripheral portion of a wafer to a desiredlevel, and a plasma processing apparatus.

In accordance with an aspect of the present disclosure, there isprovided a circular ring-shaped member for a plasma process to surrounda peripheral portion of a target substrate to be plasma-processed. Thecircular ring-shaped member includes at least one ring-shaped grooveconfigured to adjust an electric field distribution to a desireddistribution in a plasma generation space. The groove may be formed in asurface of the circular ring-shaped member and the surface may be on anopposite side to the plasma generation space. Since the ring-shapedgroove is formed in the circular ring-shaped member configured tosurround the peripheral portion of the target substrate to beplasma-processed, the electric field distribution at the peripheralportion of the target substrate can be changed.

The groove may be formed in an inner peripheral portion of the circularring-shaped member. Since the groove is formed in the circularring-shaped member in contact with the target substrate, it is possibleto adjust the electric field distribution at the peripheral portion ofthe target substrate more favorably.

Further, impedance of the circular ring-shaped member may be adjusted tobe a desired value depending on a shape of the groove. The impedancevaries depending on the shape of the groove, thereby adjusting theelectric field distribution.

The groove may be formed to have a predetermined width, starting from aposition between an inner end of the circular ring-shaped member and aposition in a range of about 30% or less of a width of the circularring-shaped member in a diametric direction. If the groove is formed ata position exceeding about 30% of the width of the circular ring-shapedmember, starting from the inner end of the circular ring-shaped memberin contact with the target substrate, it becomes difficult to adjust theelectric field distribution at the peripheral portion of the targetsubstrate.

Further, the groove may be formed to have a predetermined width which isabout 80% or less of a width of the circular ring-shaped member,starting from an inner end of the circular ring-shaped member in adiametric direction. If the groove is formed to exceed about 80% of thewidth of the circular ring-shaped member, starting from the inner end ofthe circular ring-shaped member in contact with the target substrate,the groove has less effect on the electric field distribution at theperipheral portion of the target substrate.

A depth of the groove may be about 70% or less of a thickness of thecircular ring-shaped member. When the groove is formed in the circularring-shaped member, if the depth of the groove (a length in a verticaldirection when the circular ring-shaped member is provided in ahorizontal direction) exceeds about 70% of the thickness of the circularring-shaped member, a lifetime of the circular ring-shaped member isshortened by abrasion caused by a plasma impact.

Further, the circular ring-shaped member may be made of at least one ofquartz, carbon, silicon, silicon carbide, and a ceramic material.

In accordance with another aspect of the present disclosure, there isprovided a plasma processing apparatus including a processing chamberthe inside of which is maintained in a vacuum condition; a mountingtable configured to mount thereon a target substrate and serve as alower electrode in the processing chamber; a circular ring-shaped memberprovided at the mounting table so as to surround a peripheral portion ofthe target substrate; an upper electrode arranged to face the lowerelectrode thereabove; and a power feed unit for supplying ahigh-frequency power to the mounting table. The plasma processingapparatus performs a plasma process on the target substrate by plasmagenerated in the processing chamber. The circular ring-shaped member mayinclude at least one ring-shaped groove configured to adjust an electricfield distribution to a desired distribution in a plasma generationspace. The groove may be formed in a surface of the circular ring-shapedmember and the surface may be on an opposite side to the plasmageneration space. Since the ring-shaped groove is formed in the circularring-shaped member configured to surround the peripheral portion of thetarget substrate to be plasma-processed, the electric field distributionat the peripheral portion of the target substrate can be changed.

The groove may be formed in an inner peripheral portion of the circularring-shaped member. Since the groove is formed in the circularring-shaped member in contact with the target substrate, it is possibleto adjust the electric field distribution at the peripheral portion ofthe target substrate more favorably.

Further, impedance of the circular ring-shaped member may be adjusted tobe a desired value depending on a shape of the groove. The impedancevaries depending on the shape of the groove, thereby adjusting theelectric field distribution.

The groove may be formed to have a predetermined width, starting from aposition between an inner end of the circular ring-shaped member and aposition in a range of about 30% or less of a width of the circularring-shaped member in a diametric direction. If the groove is formed ata position exceeding about 30% of the width of the circular ring-shapedmember, starting from the inner end of the circular ring-shaped memberin contact with the target substrate, it becomes difficult to adjust theelectric field distribution at the peripheral portion of the targetsubstrate.

Further, the groove may be formed to have a predetermined width which isabout 80% or less of a width of the circular ring-shaped member,starting from an inner end of the circular ring-shaped member in adiametric direction. If the groove is formed to exceed about 80% of thewidth of the circular ring-shaped member, starting from the inner end ofthe circular ring-shaped member in contact with the target substrate,the groove has less effect on the electric field distribution at theperipheral portion of the target substrate.

A depth of the groove may be about 70% or less of a thickness of thecircular ring-shaped member. When the groove is formed in the circularring-shaped member, if the depth of the groove (a length in a verticaldirection when the circular ring-shaped member is provided in ahorizontal direction) exceeds about 70% of the thickness of the circularring-shaped member, a lifetime of the circular ring-shaped member isshortened by abrasion caused by a plasma impact.

Further, the circular ring-shaped member may be made of at least one ofquartz, carbon, silicon, silicon carbide, and a ceramic material.

In accordance with the plasma processing apparatus of the presentdisclosure, the etching rate or deposition rate at the peripheralportion of the wafer can be adjusted easily and freely by adjusting theelectric field distribution at the peripheral portion of the wafer,thereby improving uniformity or production yield in the plasma process.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may best be understood by reference to the followingdescription taken in conjunction with the following figures:

FIG. 1 is a longitudinal cross sectional view showing a configuration ofa plasma processing apparatus in accordance with an embodiment of thepresent disclosure;

FIG. 2A is a cross sectional view of a conventional focus ring;

FIG. 2B is a cross sectional view of a groove-formed focus ring;

FIGS. 3A to 3C show shapes of grooves;

FIG. 4 is a graph showing an etching rate of an oxide film;

FIG. 5 is a graph showing an etching rate of a nitride film;

FIGS. 6A and 6B provide graphs showing a characteristic of a sputteringrate; and

FIGS. 7A and 7B provide graphs showing a characteristic of a depositionrate.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment applying a plasma processing apparatus inaccordance with the present disclosure to an etching apparatus will bedescribed in detail with reference to the accompanying drawings.However, the present disclosure is not limited thereto.

FIG. 1 shows a schematic overall configuration of a plasma processingapparatus 1 in accordance with the embodiment of the present disclosure.The plasma processing apparatus includes a cylindrical processingchamber the inside of which can be airtightly sealed and is made of,e.g., aluminum or stainless steel. In this case, a capacitively coupledplasma processing apparatus of a lower electrode dual frequencyapplication type is employed, but the present disclosure is not limitedthereto. For example, a plasma processing apparatus of an upper andlower electrode dual frequency application type or a plasma processingapparatus of a single frequency application type may be employed.

Within the processing chamber, a susceptor 2 configured to support asemiconductor wafer (hereinafter, referred to as “wafer”) 15 as a targetsubstrate is horizontally placed. The susceptor 2 is made of aconductive material such as aluminum and serves as an RF electrode.Installed on a top surface of the susceptor 2 is an electrostatic chuck16 made of a dielectric material such as ceramic so as to hold the wafer15 by an electrostatic attracting force. An internal electrode 17 formedof a conductive film made of a conductive material such as copper ortungsten is embedded in the electrostatic chuck 16. The susceptor 2 issupported by a cylindrical holder 3 made of an insulating material suchas ceramic. The cylindrical holder 3 is supported by a cylindricalsupport 4 of the processing chamber. Installed on a top surface of thecylindrical holder 3 is a focus ring 5 configured to surround the topsurface of the susceptor 2 in a ring shape.

Around the outside of the focus ring 5, a circular ring-shaped coverring 25 is installed.

The electrostatic chuck 16 is used as a heat exchange plate foradjusting a temperature of the wafer 15 by exchanging heat with thewafer 15 in contact with each other. The focus ring 5 serving as one ofcircular ring-shaped members for a plasma process is installed aroundthe outside of the wafer 15. In this embodiment, the single focus ring 5is provided, but it may be possible to use a double focus ring which isdivided into an outer focus ring and an inner focus ring. The focus ring5 can be made of, e.g., Si, SiC, C or SiO₂ depending on the wafer 15.

Between a sidewall of the processing chamber and the cylindrical support4, a ring-shaped exhaust line 6 is provided. At the entrance or on theway to the exhaust line 6, a ring-shaped baffle plate 7 is provided. Abottom portion of the exhaust line 6 is connected with an exhaust device9 via an exhaust pipe 8. The exhaust device 9 includes a vacuum pumpsuch as a turbo molecular pump, and, thus, a plasma processing spacewithin the processing chamber can be depressurized to a predeterminedvacuum level. Further, a gate valve 11 configured to open and close atransfer port 10 for loading/unloading the wafer 15 is installed outsidethe sidewall of the processing chamber.

A rear surface (bottom surface) of the susceptor 2 and an upperelectrode 21 are connected with upper ends of circular column-shaped orcylindrical-shaped power feed rods 14 a and 14 b extending from outputterminals of matching units 13 a and 13 b, respectively. First andsecond high frequency power supplies 12 a and 12 b used in a dualfrequency application type are electrically connected with the susceptor2 and the upper electrode 21 via the matching units 13 a and 13 b andthe power feed rods 14 a and 14 b, respectively. The power feed rods 14a and 14 b are made of a conductive material such as copper or aluminum.

The first high frequency power supply 12 a outputs a first highfrequency power having a relatively high frequency of, e.g., about 60MHz for generating plasma above the susceptor 2. The second highfrequency power supply 12 b outputs a second high frequency power havinga relatively low frequency of, e.g., about 2 MHz for attracting ions tothe wafer 15 on the susceptor 2. The matching unit 13 a performsmatching between impedance of the first high frequency power supply 12 aand impedance of a load (mainly, electrode, plasma, and chamber), andthe matching unit 13 b performs matching between impedance of the secondhigh frequency power supply 12 b and the impedance of the load.

The electrostatic chuck 16 is configured such that the internalelectrode 17 formed of a sheet-shaped or mesh-shaped conductor isembedded in a film-shaped or plate-shaped dielectric member. Theelectrostatic chuck 16 is integrally fixed to or integrally formed onthe top surface of the susceptor 2. The internal electrode 17 iselectrically connected with a DC power supply and a power feed line suchas a coated line provided outside the processing chamber, and, thus, thewafer 15 can be attracted to and held on the electrostatic chuck 16 by aCoulomb force generated by a DC voltage applied from the DC powersupply.

At a ceiling portion of the processing chamber, the upper electrode 21is provided to face parallel to the susceptor 2. The upper electrode 21is formed in a circular plate shape having a hollow structure (hollowportion) at the center thereof, and a plurality of gas discharge holes22 is formed in its bottom surface, thereby functioning as a showerhead. An etching gas supplied from a processing gas supply unit isintroduced into the hollow portion in the upper electrode 21 through agas inlet line 23 and uniformly distributed and supplied from the hollowportion to the processing chamber through the gas discharge holes 22.Further, the upper electrode 21 is made of, e.g., Si or SiC.

A heat transfer gas such as a He gas is supplied between theelectrostatic chuck 16 and the rear surface of the wafer 15 from a heattransfer gas supply unit (not illustrated) through a gas supply line 24.The heat transfer gas accelerates heat conduction in the electrostaticchuck 16, i.e., between the susceptor 2 and the wafer 15.

A main feature of this plasma processing apparatus is that the focusring 5, in which a circular ring-shaped groove is formed, is used so asto obtain an impedance characteristic capable of forming an intensityand distribution of an electric field most suitable for a characteristicof the wafer 15 or various kinds of plasma processes.

FIG. 2A is a cross sectional view of a conventional focus ring which hasbeen used in a conventional plasma process, and FIG. 2B is a crosssectional view of a groove-formed focus ring in accordance with anembodiment of the present disclosure. All the focus rings illustrated inFIGS. 2A and 2B are single (or referred to as “integrated type”) focusrings. However, the present disclosure is not limited to the singlefocus ring and, for example, may be applied to either or both of twoseparate focus rings which are divided into an inner focus ring and anouter focus ring. The focus ring may be made of, for example, the samematerial (Si) as the wafer 15, or any one of quartz, carbon, siliconcarbide, and ceramic materials (yttria (Y₂O₃) or silica). The focus ring5 is mounted on the electrostatic chuck 16 so as to support a peripheralend portion of the wafer 15.

There will be explained the groove-formed focus ring in accordance withthe embodiment of the present disclosure with reference to FIG. 2B. Inthe groove-formed focus ring illustrated in FIG. 2B, a groove 51 isformed on a surface (rear surface of the focus ring) in contact with theelectrostatic chuck 16. Desirably, such a groove may be formed on therear surface of the focus ring. That is because that if a groove-formedsurface is exposed to plasma ions, the groove may be eroded (worn out)by a plasma ion impact and, thus, a shape of the groove may be deformed.Further, that is because that if the groove is formed by a cuttingprocess or the like, dust caused by the plasma ion impact may be highlygenerated as compared to the other surface.

In FIG. 2B, a depth of the groove 51 (length in a vertical directionwhen the focus ring 5 is installed in a horizontal direction) isdesirably about 70% or less of a thickness of the focus ring and moredesirably about 50% or less. If the depth of the groove 51 exceeds about70%, a lifetime of the focus ring 5 may be shortened by abrasion causedby a plasma impact. Further, in order to secure hardness of the focusring, the depth of the groove is desirably about 70% or less.Furthermore, the depth of the groove 51 of the groove-formed focus ringillustrated in FIG. 2B is about 0.4 mm, which is about one-ninth ( 1/9)of a thickness of the focus ring 5, i.e., about 3.6 mm.

Moreover, a width of the groove 51 in a diametric direction may be about80% or less of a width of the focus ring in a diametric direction. Forexample, the width of the groove 51 of the groove-formed focus ringillustrated in FIG. 2B is about 40 mm, which corresponds to abouttwo-fifth (⅖) (40%) of a width of the focus ring 5, i.e., about 100 mm.

In addition, the groove 51 may be formed from an end of the focus ringat the install position of the wafer 15 or from a position in the rangeof about 30% or less of the width of the focus ring in a diametricdirection. That is because that by forming the groove 51 from the endportion as close as possible, in such a range that is not affected bythe ion impact, an electric field distribution on a surface of the wafer15 can be adjusted more easily.

As described above, the groove 51 may be formed in a certain shapesuitable to optimize the electric field distribution on the surface ofthe wafer 15. FIGS. 3A to 3C show shapes of grooves in accordance withthe present disclosure. FIG. 3A shows a case where a groove 51 is formedin a semi-elliptic shape from the vicinity of an inner end portion of afocus ring 5. FIG. 3B shows a case where a trapezoid-shaped groove 51 isformed at an inner end portion of a focus ring 5 and a rectangulargroove 51 is formed outside thereof in a diametric direction. Further,FIG. 3C shows a case where three circular hollow grooves 51 aresuccessively formed inside a focus ring 5. The present disclosure isrelated to a technique of forming a groove in a focus ring so as toobtain a desired electric field distribution, and, thus, it may bepossible to form an optimal groove for a desired electric fielddistribution.

Experimental Example 1

As a focus ring to be installed in the plasma processing apparatus 1, acouple of the focus rings 5 illustrated in FIG. 2B were prepared. A heattransfer sheet having a heat conductivity of about 1 W/MK was almostfully filled in a groove 51 of one focus ring. It will be referred to as“groove-formed focus ring of 1 W type” in the specification hereinafter.Further, a heat transfer sheet having a heat conductivity of about 17W/MK was almost fully filled in a groove 51 of the other focus ring. Itwill be referred to as “groove-formed focus ring of 17 W type” in thespecification hereinafter. Furthermore, as a comparative example, theconventional focus ring illustrated in FIG. 2A was prepared. It will bereferred to as “conventional focus ring” in the specificationhereinafter.

Then, three sheets of blanket wafers (hereinafter, referred to as “waferOx”) having a diameter of about 300 mm with an oxide film formed thereonand three sheets of blanket wafers (hereinafter, referred to as “waferNi”) having a diameter of about 300 mm with a nitride film formedthereon were prepared. The conventional focus ring, the groove-formedfocus ring of 1 W type, and the groove-formed focus ring of 17 W typewere installed around the blanket wafers Ox and Ni, respectively; aprocessing gas of C₄F₆/Ar/O₂(18/225/10) was supplied; and a plasmaprocess was performed on each of the wafers Ox and the wafers Ni forabout 60 seconds. Here, a temperature of an upper electrode, atemperature of a wall surface of a processing chamber, and a temperatureof a bottom surface of an electrostatic chuck were about 60° C., 60° C.,and 45° C., respectively.

FIG. 4 is a graph showing etching rates of the wafers Ox and FIG. 5 is agraph showing etching rates of the wafers Ni under the above-describedplasma process conditions. In the horizontal axis of the graphs in FIGS.4 and 5, a point “O” represents a central point of the wafer and theright and left sides in a diametric direction from that point arerepresented in millimeters up to 150 mm. The vertical axis represents anetching rate (nm/min) of an oxide film or an etching rate (nm/min) of anitride film.

As depicted in FIG. 4, when the conventional focus ring was installedaround the wafer Ox and the plasma process was performed thereon, anetching rate of the oxide film is about 187 nm/min at the centralportion of the wafer and is increased toward the end portion thereof. Ata position about 30 mm away from the end portion of the wafer, theetching rate has the maximum value of about 195 nm/min. From thatposition to the farthest end portion, the etching rate is approximatelyconstant.

Meanwhile, when the groove-formed focus ring of 1 W type was installedaround the wafer Ox and the plasma process was performed thereon, theetching rate is approximately the same as the etching rate (about 187nm/min) of the conventional focus ring at the central portion of thewafer, but the etching rate is increased toward the end portion thereof.At a position about 30 mm away from the end portion of the wafer, theetching rate is about 197 nm/min. From that position to the farthest endportion, the etching rate is sharply increased and is about 218 nm/minat the farthest end portion.

The etching rate of the groove-formed focus ring of 17 W type hasapproximately the same characteristic as that of the groove-formed focusring of 1 W type as illustrated in FIG. 4.

FIG. 5 is a graph showing an etching rate of a nitride film when theconventional focus ring was installed around the wafer Ni and the plasmaprocess was performed under the above-described conditions. As shown inFIG. 5, the etching rate is about −2 nm/min at the central portion ofthe wafer, which means that CxFy has been deposited at the centralportion of the wafer. Further, the etching rate is decreased to a largerminus value (deposition rate of CxFy is increased) toward the endportion thereof. From a position about 50 mm away from the end portionof the wafer to the farthest end portion, the deposition rate isincreased.

Meanwhile, when the groove-formed focus ring of 1 W type was installedaround the wafer Ni and the plasma process was performed thereon, theetching rate has a slightly bigger minus value (about −4 nm/min) at thecentral portion of the wafer than that of the conventional focus ring.However, the etching rate comes to have plus values from minus values asit goes to the end portion. That is, at a position about 25 mm away fromthe end portion of the wafer, the deposition rate and the etching ratebecomes substantially the same, and the etching rate is increased towardthe end portion of the wafer from that position.

The etching rate of the groove-formed focus ring of 17 W type on thewafer Ni has a different etching rate but approximately the samecharacteristic as that of the groove-formed focus ring of 1 W type.

In view of the foregoing, the following facts have been proved. Adifference in the heat conductivity of the heat transfer sheet embeddedin the groove 51 does not make a big difference in the etchingcharacteristic. That is because that the groove 51 formed in the focusring 5 does not cause a change in its heat capacity but causes a changein the impedance of the focus ring 5, so that an electric fielddistribution in its vicinity is varied by a change of the impedance. Asa result, an intensity of the plasma (electric charge) impact on thewafer 15 is changed. Therefore, if a shape of the groove 51 is changedso as to obtain a desired electric field distribution according to amaterial to be plasma-processed, a desired electric field distributioncan be formed at a desired position. Accordingly, the plasma process canbe uniformly performed on the wafer 15.

Experimental Example 2

Subsequently, as a focus ring 5 to be installed in the plasma processingapparatus 1, the groove-formed focus ring of 1 W type and thegroove-formed focus ring of 17 W type were prepared in the same manneras experimental example 1, and as a comparative example thereof, theconventional focus ring was also prepared to find characteristics of asputtering rate.

Then, three sheets of blanket wafers having a diameter of about 300 mmwere prepared in the same manner as the experimental example 1.Thereafter, the conventional focus ring, the groove-formed focus ring of1 W type, and the groove-formed focus ring of 17 W type were installedaround the blanket wafers, respectively; a plasma processing chamber wasdepressurized to about 35 millitorr; a processing gas of Ar/O₂ (1225/15)was supplied; and a plasma process was performed on each of the blanketwafers for about 60 seconds. Here, a temperature of an upper electrode,a temperature of a wall surface of the processing chamber, and atemperature of a bottom surface of an electrostatic chuck were about 60°C., 60° C., and 45° C., respectively.

FIGS. 6A and 6B are graphs each showing a characteristic of a sputteringrate in case of using the above-described three kinds of focus ringsunder the above-stated plasma process conditions. In the horizontal axisof the graphs in FIGS. 6A and 6B, a point “O” represents a central pointof the wafer and the right and left sides in a diametric direction fromthat point are represented in millimeters up to 150 mm. The verticalaxis represents a sputtering rate in a unit of nm/min.

As shown in FIG. 6A, when the conventional focus ring was installedaround the blanket wafer and the plasma process was performed thereon,the sputtering rate is about 15 mm/min at the central portion of thewafer and is decreased toward the end portion thereof. From a positionabout 40 mm away from the end portion of the wafer, the sputtering rateis sharply decreased and is about 13 nm/min at the farthest end portion.

Meanwhile, when the groove-formed focus ring of 1 W type was installedaround the blanket wafer and the plasma process was performed thereon,the sputtering rate is about 17 nm/min at the central portion of thewafer. From a position about 40 mm away from the end portion of thewafer, the sputtering rate is gradually decreased. However, from aposition about 10 mm away from the end portion of the wafer to thefarthest end portion, the sputtering rate is increased and is about 19nm/min at the farthest end portion, which shows a characteristiccontrary to that of the conventional focus ring.

The sputtering rate of the groove-formed focus ring of 17 W type hasapproximately the same characteristic as that of the groove-formed focusring of 1 W type.

FIG. 6B is a graph showing normalized sputtering rates in case of usingthe three kinds of focus rings illustrated in FIG. 6A. As shown in FIG.6B, a difference in the heat conductivity of the heat transfer sheetembedded in the groove 51 does not make a big difference in thesputtering rate characteristic. Therefore, the groove 51 formed in thefocus ring 5 does not cause a change in its heat capacity but causes achange in the impedance of the focus ring 5, so that an electric fielddistribution in its vicinity can be varied by the change of theimpedance. As a result, it is deemed that an intensity of the plasmaimpact is changed, resulting in a change of the sputtering rate.

Experimental Example 3

Subsequently, as a focus ring 5 to be installed in the plasma processingapparatus 1, the groove-formed focus ring of 1 W type and thegroove-formed focus ring of 17 W type were prepared in the same manneras experimental examples 1 and 2, and as a comparative example thereof,the conventional focus ring was prepared to find characteristics of adeposition rate.

Then, three sheets of blanket wafers having a diameter of about 300 mmwere prepared. The conventional focus ring, the groove-formed focus ringof 1 W type, and the groove-formed focus ring of 17 W type wereinstalled around the blanket wafers, respectively; a plasma processingchamber was depressurized to about 35 millitorr; a processing gasincluding C₄F₆/Ar (18/1225) was supplied; and a plasma process wasperformed on each of the blanket wafers for about 60 seconds. Here, atemperature of an upper electrode, a temperature of a wall surface ofthe processing chamber, and a temperature of a bottom surface of anelectrostatic chuck were about 60° C., 60° C., and 45° C., respectively.

FIGS. 7A and 7B are graphs each showing a characteristic of a depositionrate when the above-described three kinds of focus rings, i.e., theconventional focus ring, the groove-formed focus ring of 1 W type, andthe groove-formed focus ring of 17 W type, were installed around each ofthe blanket wafers under the above-stated plasma process conditions. Inthe horizontal axis of the graphs in FIGS. 7A and 7B, a point “O”represents a central point of the wafer and the right and left sides ina diametric direction from that point are represented in millimeters upto 150 mm. The vertical axis represents a deposition rate in a unit ofnm/min.

As shown in FIG. 7A, when the conventional focus ring was installedaround the blanket wafer and the plasma process was performed thereon,the deposition rate is about nm/min at the central portion of the waferand is gradually increased toward the end portion thereof. From aposition about 50 mm away from the end portion of the wafer, thedeposition rate is sharply increased and is about 105 nm/min at thefarthest end portion.

Meanwhile, when the groove-formed focus ring of 1 W type was installedaround the blanket wafer and the plasma process was performed thereon,at the central portion of the wafer, the deposition rate is about 80nm/min, which is approximately the same deposition rate as that of theconventional focus ring. However, on the contrary to the conventionalfocus ring, from a position about 50 mm away from the end portion of thewafer, the deposition rate is decreased and is about 70 nm/min at thefarthest end portion.

The deposition rate of the groove-formed focus ring of 17 W type hasapproximately the same characteristic as that of the groove-formed focusring of 1 W type as depicted in FIG. 7A.

FIG. 7B is a graph showing normalized deposition rates of the threekinds of focus rings illustrated in FIG. 7A. As can be seen from FIG.7B, a difference in the heat conductivity of the heat transfer sheetembedded in the groove 51 does not make a big difference in thedeposition rate characteristic as mentioned in experimental examples 1and 2. Therefore, the groove 51 formed in the focus ring 5 does notcause a change in its heat capacity but causes a change in the impedanceof the focus ring 5, so that an electric field distribution in itsvicinity can be varied by the change of the impedance. As a result, itis deemed that an intensity of the plasma impact is changed, resultingin a change in the deposition rate.

In view of the foregoing, by forming a groove in a focus ring andchanging a shape of the groove, a desired electric field distributioncan be formed at a desired position. Therefore, it is obvious that anetching rate or a deposition rate can be adjusted to be a desired valueat a desired position.

The present disclosure is not limited to a plasma etching apparatus butcan be applied to other plasma processing apparatuses for plasma CVD,plasma oxidation, plasma nitridation, sputtering or the like. Further, atarget substrate of the present disclosure is not limited to asemiconductor wafer but can be any one of various kinds of substratesfor flat panel display, a photo mask, a CD substrate, and a printsubstrate.

1. A circular ring-shaped member for a plasma process provided tosurround a peripheral portion of a target substrate to beplasma-processed, the member comprising: at least one ring-shaped grooveconfigured to adjust an electric field distribution to a desireddistribution in a plasma generation space, wherein the groove is formedin a surface of the circular ring-shaped member and the surface is on anopposite side to the plasma generation space.
 2. The circularring-shaped member of claim 1, wherein the groove is formed in an innerperipheral portion of the circular ring-shaped member.
 3. The circularring-shaped member of claim 1, wherein impedance of the circularring-shaped member is adjusted to be a desired value depending on ashape of the groove.
 4. The circular ring-shaped member of claim 1,wherein the groove is formed to have a predetermined width, startingfrom a position between an inner end of the circular ring-shaped memberand a position in a range of about 30% or less of a width of thecircular ring-shaped member in a diametric direction.
 5. The circularring-shaped member of claim 1, wherein the groove is formed to have apredetermined width which is about 80% or less of a width of thecircular ring-shaped member, starting from an inner end of the circularring-shaped member in a diametric direction.
 6. The circular ring-shapedmember of claim 1, wherein a depth of the groove is about 70% or less ofa thickness of the circular ring-shaped member.
 7. The circularring-shaped member of claim 1, wherein the circular ring-shaped memberis made of at least one of quartz, carbon, silicon, silicon carbide, anda ceramic material.
 8. A plasma processing apparatus comprising: aprocessing chamber the inside of which is maintained in a vacuumcondition; a mounting table configured to mount thereon a targetsubstrate and serve as a lower electrode in the processing chamber; acircular ring-shaped member provided at the mounting table so as tosurround a peripheral portion of the target substrate; an upperelectrode arranged to face the lower electrode thereabove; and a powerfeed unit for supplying a high frequency power to the mounting table,wherein the plasma processing apparatus performs a plasma process on thetarget substrate by plasma generated in the processing chamber, thecircular ring-shaped member includes at least one ring-shaped grooveconfigured to adjust an electric field distribution to a desireddistribution in a plasma generation space, and the groove is formed in asurface of the circular ring-shaped member and the surface is on anopposite side to the plasma generation space.
 9. The plasma processingapparatus of claim 8, wherein the groove is formed in an innerperipheral portion of the circular ring-shaped member.
 10. The plasmaprocessing apparatus of claim 8, wherein impedance of the circularring-shaped member is adjusted to be a desired value depending on ashape of the groove.
 11. The plasma processing apparatus of claim 8,wherein the groove is formed to have a predetermined width, startingfrom a position between an inner end of the circular ring-shaped memberand a position in a range of about 30% or less of a width of thecircular ring-shaped member in a diametric direction.
 12. The plasmaprocessing apparatus of claim 8, wherein the groove is formed to have apredetermined width which is about 80% or less of a width of thecircular ring-shaped member, starting from an inner end of the circularring-shaped member in a diametric direction.
 13. The plasma processingapparatus of claim 8, wherein a depth of the groove is about 70% or lessof a thickness of the circular ring-shaped member.
 14. The plasmaprocessing apparatus of claim 8, wherein the circular ring-shaped memberis made of at least one of quartz, carbon, silicon, silicon carbide, anda ceramic material.